1. Heat oven to 350°F. Grease bottoms only of 2 (8- or 9-inch) round cake pans with shortening or cooking spray.
2. In large bowl, beat yellow cake ingredients with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Set aside.
3. In another large bowl, beat devil's food cake ingredients on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
4. Spoon yellow and devil's food batters alternately into pans, dividing evenly. Cut through batters with table knife in zigzag pattern for marbled design.
5. Bake 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool in pans on cooling racks 15 minutes. Remove from pans. Cool completely, top sides up, about 1 hour.
6. In medium bowl, beat powdered sugar and 1/3 cup butter with spoon or electric mixer on low speed until blended. Stir in 2 teaspoons vanilla and the chocolate. Gradually beat in just enough milk to make frosting smooth and spreadable.
7. On serving plate, place 1 cake, rounded side down (trim rounded side if necessary so cake rests flat). Spread with 1/4 cup frosting. Top with second cake, rounded side up. Frost side and top of cake with remaining frosting.
1 Serving: Calories 490 (Calories from Fat 190); Total Fat 21g (Saturated Fat 12g, Trans Fat 1/2g); Cholesterol 120mg; Sodium 430mg; Total Carbohydrate 70g (Dietary Fiber 1g, Sugars 45g); Protein 4g Percent Daily Value*: Vitamin A 10%; Vitamin C 0%; Calcium 2%; Iron 10% Exchanges: 1 1/2 Starch; 3 Other Carbohydrate; 0 Vegetable; 4 Fat Carbohydrate Choices: 4 1/2
*Percent Daily Values are based on a 2,000 calorie diet.